@Jeremy : It's not normal to be unable to idle your engine; You either have air/fuel problems or clutch problems. Most commonly it will be a problem with the clutch cable tension, it might be necessary to open the clutch cover and remove a notch on the flower nut. Also, you might have an air leak which could cause all sorts of symptoms such as the engine still revving for a few seconds after releasing the throttle. Also, yes a centrifugal clutch would allow to idle a chinagirl/HT engine without using the clutch.